Conventionally used hose clamps are formed by bending a metal strip into an annular shape. One of such hose clamps has two ends from which first and second operating pieces are raised respectively. The operating pieces are pinched so that the entire hose clamp is diameter-enlarged so as to be put onto a hose or the like or diameter-reduced so as to clamp the hose or the like. Further, another conventionally known hose clamp has a triangular opening which is formed therethrough to extend in a lengthwise direction in a developed state. Undermentioned Patent Document 1 discloses an example of the hose clamp with the triangular opening.